feat: Animation current time methods

[eonarheim]

===:clipboard: PR Checklist :clipboard:===

• 📌 issue exists in github for these changes
• 🔬 existing tests still pass
• 🙈 code conforms to the style guide
• 📐 new tests written and passing / old tests updated with new scenario(s)
• 📄 changelog entry added (or not needed)

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This PR adds new property and methods overloads to ex.Animation

• ex.Animation.currentFrameTimeLeft will return the current time in milliseconds left in the current
• ex.Animation.goToFrame(frameNumber: number, duration?: number) now accepts an optional duration for the target frame